The idea behind Semantic Web technology appeared when Berners-Lee, Hendler, & Lassila (2001) mentioned it in their paper, “The semantic Web” in 2001. The basic idea of Semantic Web is to present information that can be understood not only by human, but also by computer (machine readable); therefore, they defined Semantic Web as “an extension of the traditional Web in which information is given well-defined meaning, better enabling computers and people to work in cooperation”. By its definition, it appears that Semantic Web technology is not a kind of rocket science technology, but a complementary layer for an existing web technology.
With the billions of web pages available on the Internet nowadays, it is a job of Semantic Web technology to extract the meaning of those heterogeneous interlinked pages, and play as a mediator for users who needs those information. At the end of the story, Semantic Web technology will enable a querying, where an agent gathers information presented at different resources on the Web and returns accurate information to the user (Hella, 2014).
To achieve that vision, the concept of Semantic Web technology is supported by several technologies. Those are URI, XML and XML Schema, RDF and RDF Schema, and Ontology. The following sections will give a short overview of the notion of each of them.

URI
URI is an abbreviation of Universal Resource Identifier. It is meant to identify any resource on Internet including web page, image, music file, video, and service. Since anything can be linked to anything, URI is a powerful tool to explain about the concept or entity or object that anyone can find on the Internet. In addition, by using different URI, we can make each object unique that can deﬁne diverse objects such as telephone numbers, ISBN numbers, and geographic locations (Antoniou & Van Harmelen, 2004).

XML and XML Schema
XML or eXtensible Markup Language is a language describes a class of data objects called XML documents and partially describes the behavior of computer programs which process them (Bray et al., 1998). XML exist to overcome a classic problem of HTML, which is HTML document does not contain structural information, that is, information about pieces of the document and their relationships (Antoniou & Van Harmelen, 2004). XML document, on the other hand, is a structured document that can be easily read by machine (computer). In fact, the relation between tags can (sometimes) be understood in the nested document itself. One benefit of XML is it allows everyone to create their own tags for annotation purpose. These tags are hidden in sections of text on a web page.

In addition, the use of XML nowadays is mostly for data exchange between applications. Therefore, XML is well known as a uniform data exchange format or intermediate language for exchanging data. However, although the XML document is well structured, it actually does not carry any meaning.

Next to XML, there is a XML Schema that provides a certain mechanism to define grammars for legal XML documents (Hella, 2014). One example is the use of namespace mechanism. The use of namespace is important in the concept of Semantic Web because it provides a way to uniquely identify an object or entity or thing or concept on web.